(57) When a driver depresses an accelerator pedal finely to drive his vehicle a little distance forward repeatedly on a busy road, the ordinary accelerator pedal control characteristics are automatically changed to fine control characteristics such that opening rate of the throttle valve increases relatively gently with increasing accelerator pedal stroke. The control characteristics are changed from the ordinary ones to the fine ones, when both of detected accelerator pedal stroke and stroke speed do not exceed the predetermined reference values within a predetermined time period after the accelerator pedal has been depressed.